Asymmetric reduction of 2-substituted 2-butenolides with reductase from Marchantia polymorpha

A p68 reductase participating in the asymmetric reduction of the C–C double bond of 2-substituted 2-butenolides was isolated from Marchantia polymorpha. The enzyme reduced 2-substituted 2-butenolides to give (R)-butanolides, and the reduction of citraconic anhydride afforded (R)-methylsuccinic anhydride.     

Studies on cardiac ingredients of plants. VII: Chemical transformation of proscillaridin by means of the Diels-Alder reaction and biological activities of its derivatives.

The Diels-Alder reactions of a cardiac glycoside, proscillaridin (1), with some dienophiles were investigated. The reaction of 1 with alkenes such as methyl vinyl ketone and methyl acrylate afforded 3-oxo-2-oxabicyclo[2.2.2]oct-7-enes (2-5) and para-substituted benzene derivatives (6 and 7), while 1 reacted with alkynes (3-butyn-2-one, methyl propiolate) to yield para- or meta-substituted benzene derivatives (6-9). The biological activities of the resulting derivatives were evaluated by the use of isolated guinea-pig papillary muscle preparations and Na+,K(+)-adenosine triphosphatase (ATPase) preparation from dog kidney. Among the proscillaridin derivatives, compounds 4 and 7 moderately inhibited Na+,K(+)-ATPase activity. Furthermore, the concentration range of 7 over which its positive inotropic effect on guinea-pig papillary muscle preparations, increased from 5% to 95% of maximum was broader than that of 1, i.e., concentration dependency was maintained over a greater range of concentration.     

Synthesis and characterization of norbornene–ethylene–styrene terpolymers with a substituted ansa‐fluorenylamidodimethyltitanium‐based catalyst

This article reports a synthetic method for a norbornene–ethylene–styrene (N‐E‐S) terpolymer, which has not been well investigated so far, via incorporation of styrene (S) into vinyl‐type norbornene–ethylene (N‐E) copolymers catalyzed by a substituted ansa‐fluorenylamidodimethyltitanium [Me₂Si(3,6‐tBu₂Flu)(tBuN)]TiMe₂ catalyst ( I ) activated with a [Ph₃C][B(C₆F₅)₄]/Al(iBu)₃ cocatalyst at room temperature in toluene. The resulting terpolymerization product contained the targeted N‐E‐S terpolymer and the contaminated homopolymers, which were then able to be completely removed by solvent fractionation techniques. While homopolystyrene was easily extracted by fractionation with methylethylketone as a soluble part, homopolyethylene and a trace amount of homopolynorbornene could be perfectly separated by fractionation with chloroform as insoluble parts. The detail characterizations of a chloroform‐soluble polymer with gel permeation chromatography, nuclear magnetic resonance, and differential scanning calorimetry analyses proved that it contained a true N‐E‐S terpolymer with long N‐E sequences incorporated with isolated or short styrene sequences. The homogeneity of the morphology together with a single glass transition temperature that proportionally decreased with the increase of the styrene contents indicated that the N‐E‐S terpolymer obtained in this work is a random polymer with an amorphous structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2765–2773, 2007     

DNA cleavage induced by thermal electron transfer from a dimeric NADH analogue to acridinium ions in the presence of oxygen

Acridinium ions, which can intercalate to DNA, act as thermal DNA cleavers in the presence of a dimeric NADH analogue and O2 in an aqueous solution via thermal electron transfer from a dimeric NADH analogue to acridinium ions, followed by the electron-transfer reduction of O2 to O2*- by the resulting NAD radicals.     

Structures and cytotoxic activity relationship of casearins, new clerodane diterpenes from Casearia sylvestris Sw

Casearins G-R, new cytotoxic clerodane diterpenes have been isolated from the leaves of Casearia sylvestris Sw. (Flacourtiaceae). Their structures have been elucidated by spectroscopic methods and chemical conversions, and their structure-activity relationships have been discussed.     

A new strategy for construction of eight-membered carbocycles by Brook rearrangement mediated [6 + 2] annulation

[reaction: see text] A newly developed strategy for construction of eight-membered carbocycles via [6 + 2] annulation that involves the combination of beta-alkenoyl acylsilanes and a vinyllithium derivative is described. A unique feature of this annulative approach is that it enables in one operation and a stereoselective manner construction of eight-membered ring systems containing useful functionalities for further synthetic elaboration from readily available six- and two-carbon components.     

Stereochemistry in cationic polymerization of alkenyl ethers. V. Stereochemistry of acetal additions as model reactions for the polymerization of alkenyl ethers

Acetal additions to β-substituted vinyl ethers having a variety of substituents (alkenyl ethers) were stereochemically investigated as model reactions for their cationic polymerization. The reactions catalyzed by BF₃O(C₂H₅)₂ in CH₂Cl₂ at O°C gave 1:1 adducts, the steric structure of which was determined by means of ¹³C-NMR spectroscopy. trans-Alkenyl ethers always gave adducts with a single structure stereospecifically, indicating that the intermediate carbocation attacks a trans-alkenyl ether from a definite direction independent of the bulkiness of substituents. On the other hand, cis-alkenyl ethers formed adducts with two steric structures, and the direction of cation addition was found to depend on the bulkiness of the alkoxy group involved. The above trends were in agreement with the results for poly(alkenyl ether)s and allowed detailed discussion of the stereochemistry of the propagation processes in alkenyl ether polymerizations.     

Nitrile anion cyclization with epoxysilanes followed by brook rearrangement/ring opening of cyclopropane nitriles/alkylation

The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives with a base and an alkylating agent affords delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of the cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring.     

Mechanism of stereoregular polymerization of butadiene by homogeneous Ziegler-Natta catalysts. I. Effects of the species of transition metals

Butadiene was polymerized by catalysts of the type: metal acetylacetonate (metal: Ti to Ni in the periodic table)–triethylaluminum–aluminum halide, with various ratios of triethylaluminum to aluminum halide. The minimum cis content was observed with vanadium catalyst in all cases, while the minimum polymer yields were observed with the iron and the manganese catalysts. These transition metal effects are discussed in terms of the crystal field theory, and it is suggested that the electrostatic interaction between the nearly nonbonding electrons of transition metal atom and a butadiene molecule or a growing end of the polymeric chain plays an important role in the stereoregular polymerization of butadiene by homogeneous Ziegler-Natta catalysts.